I have tried the Genelax Lion El84 alongside NOS Mullard, Amperex and Mullard (reissue)...and have to say its the one I like the least on my Leben cs-300x. I have tried it with Sylvania 5751 blackplates, RCA command 5751, Raytheon 5751, GE 5751 Blackplates and the Raytheon 7729...and none of these could make them sing.

I am not very good with describing sound quality...but simply put I am yet to hear an el84 type which can match the Amperex for midrange quality and tonal richness. Matching them with the right pre-amp tubes (read Raytheon 7729) has given me the most satisfying eargasm yet... . I suspect they may even flatter some of the less esoteric 12ax7 or 5751 types.

The Raytheon 7729, Sylvania Bk Plate 5751 and RCA command 5751 are all great tubes. But if I have to pick one that would be the Raytheon 7729...by far the best 12ax7 or 5751 I have heard. They are extremely hard to find though (almost extinct).

If I did not have the 7729 then my order of preference would be;

Raytheon 5751 windmill getter with Amperex

RCA command 5751 with the Amperex

Sylvania 5751 Blackplate with the Mullard (reissue)

Sylvania 5751 Blackplate with NOS Mullard

The sylvania 5751's with the Amperex did not quite float my boat though...the midrange presentation way too forward to my liking

The Raytheon Windmill-getter 5751 are my favorite driver tube in the Leben, for sure. I like the Philips-Holland EL84 a lot, but when I put in the GE 6BQ5, for some reason I haven't wanted to take them out!

The Raytheon Windmill-getter 5751 are my favorite driver tube in the Leben, for sure. I like the Philips-Holland EL84 a lot, but when I put in the GE 6BQ5, for some reason I haven't wanted to take them out!

I have heard a lot of good things about GE 6bq5. I read somewhere that you get most tone for the money with them... I will give them a try soon

Any Amperex tube made in Holland is really a Philips tube, since Amperex was a US company originally, but was then bought by Royal Dutch Philips. So Amperex Holland tubes are essentially Philips tubes.

Now all that said, yes, I believe the Philips tubes I have are the same as the Amperex you are referring to.

Hi. I've been lurking around Head-Fi for a couple years and really haven't posted that much. But I recently bought and received (today) a Leben CS300XS. I'm having some issues with the amp, which I already raised with my dealer and distributor and they do have me covered, though I'll have to wait a few weeks and live with the current amp in the meantime. However, the two issues are perplexing, and being somewhat reluctant to give up and wait.... I would love advice should anyone here have insight.

First, the amp sounds mostly fantastic. This is the best integrated and headphone amp I have owned. I was dazzled by feeling "in the music" today while listening to The Beatles 2009 Mono Box Set remasters through speakers.

Second, I have somewhat of a developed and trained ear being a musician for quite some time. I can hear differences in tubes and cables easily and this perception comes from years of playing guitar and using tube amps, and trying gear and listening carefully. If something sounds different or "off" I'll generally hear it.

Third, I realize my particular quesions may eventually turn into a technical / troubleshooting thread probably best placed in some other area of Head-Fi, BUT.... I beg leniency and would like to start here because I'm new to Leben, and hopefully this large thread has enough expertise to either lend appropriate advice on my issues as related to the CS300XS, and/or eventually point me in the right direction.

Now the issues...

The first issue - My 600ohm AKG K240M (made in Austria) phones are significantly lower in volume in the left channel through the CS300XS. I have ruled out the phones. They work with several other amps. Stereo separation is accurate, confirmed with other amps. Not the best phones, I know, but I have had them for years and years for mixing music and they are accurate and typically un-hyped / flat. Likewise my 32ohm Shure E4C (IEM) is slightly lower volume in the same left channel but only slightly compared to the AKGs. Again, it works fine with other amps.

I have ruled out IC's, source, input selection on the Leben, etc. I even swapped tubes from left to right, both the power and preamp tubes, first independently (EL84s only), then together (5751s & EL84s). The issue stayed on the left, regardless of tubes.

The second issue - while the amp sounds mostly fantastic with speakers, I have noticed that the opposite channel (right) has slightly diminished bass response. I'm estimating around 2-3db. I have asked a second party to listen and they confirmed. Just ruling out my hearing... :) Again, this issue persists regardless of IC's, source, input selection on the Leben, and especially regardless of the speakers, which I swapped from left to right to rule them out. I confirmed the diminished bass using mono recordings and panning the balancer from hard left to hard right. The right definitely has lower bass response with the same monaural source material.

To summarize - left channel with phones is lower volume - significantly lower with 600ohm AKGs. The same left channel has roughly even volume to the right channel when using speakers, but the right channel has slightly less bass or low freq. response with speakers, around 2-3db down.

Any insights? With the quality of this amp as high as it is, it seems highly unlikely something silly is in play like mis-wiring or cold solder joints. My gut says maybe the Leben doesn't like my two particular models of headphones. But why manifest as lower volume in just one channel, and then the opposite channel has less bass with speakers. Odd, and confounding. Any insights are welcomed and will be appreciated.

Starfish...have you checked the impedence matching switch in the rear binding post. I must be set to the highest impedence for headphones. Not sure if this will solve your problem though...but worth checking.

Thanks for the suggestion. Yes, I had checked out the impedance switch. It was set to 8ohm which matches my speakers and is also the highest available.

I also tried flipping /cycling the headphone switch, input switch and impedance switches about 20 times each in case there was an intermittent or dirty contact somewhere. This had no effect on either issue. Also, the impedance switch seems to have no audible impact on headphones nor speakers in any position (4/6/8 ohm).

I also checked my AKG phones with a multimeter set to continuity to make sure there is no leak between left / right / shield. There is not. My meter's continuity test also gives resistance while in continuity mode, which measured 575 ohms for each side. These were brief tests so as not to damage the phones.

Sounds like an amp problem to me. But there is no channel imbalance with speakers?

One thing to point out - the Leben is really not designed for 600 ohm headphones. It should work, but the headphone out is a 32 ohm secondary winding from the output transformer. Leben's testing of the headphone out was done with 32 ohm headphones. They have said publicly that it should drive any headphone fine, but that they designed it around lower impedance headphones. And the best results for me have been with headphones under 120 ohms or so.Edited by Skylab - 9/29/11 at 6:26am

Ok, thanks. There is not a volume imbalance with speakers but there is a difference in bass or lower frequencies. The left has more bass with speakers and this is odd since it is the affected channel with headphones. I have tried swapping the speakers from left to right to be sure it wasn't the speaker, and it is not. I have also fully swapped out all the tubes and the same issues occur.

The 600ohm AKGs do drive fine in the right side - the quality is very good and plenty of volume at about 9:00 on the volume pot. It's just that the left side is probably 1/4 the volume of the right side. I've just never seen an issue like this before. Typically the entire cans will be reduced not just one side. Odd issue for certain.